HIGH VOLTAGE ENGINEERING(3:1:0), - Veer …

1 high VOLTAGE engineering (3:1:0), 8th Sem. ( electrical ), VSSUT MODULE-I (10 HOURS) Conduction and breakdown in gases: Gases as insulating media, Ionisation processes. Townsend current growth equation. Current growth in the presence of secondary processes. Townsend s criterion for breakdown. Experimental determination of ionization coefficients. Breakdown in electronegative gases, time lags for breakdown, streamer theory of breakdown in gases, Paschen s law, Breakdown in non-uniform field and corona discharges, Post breakdown phenomena and applications, practical considerations in using gases for insulation purposes.

2 MODULE-II (10 HOURS) Conduction and breakdown in liquid dielectrics: Pure liquids and commercial liquids, conduction and breakdown in pure liquids. Breakdown in solid dielectrics: Introduction, Intrinsic brakdown. Electromechanical breakdown, Thermal Breakdown of solid dielectrics in practice. MODULE-III (10 HOURS) Generation of high VOLTAGE and currents: Generation of high , voltages, Generation of high alternating voltages, Generation of Impulse voltages. Tripping and control of impulse generators.

3 Generation of Impulse currents. Measurements of high voltages and currents: Measurement of high voltages. Measurement of high and impulse voltages. Measurement of high and impulse currents, cathode ray oscillographs for impulse voltages and currents measurements. MODULE-IV (10 HOURS) Non destructive testing of materials and electrical apparatus: Introduction. Measurement of resistivity. Measurement of dielectric constant and loss factor. Partial discharge measurements.

4 high VOLTAGE testing of electrical apparatus: Testing of insulators and bushings. Testing of isolators and circuit breakers, cables. Testing of transformers, surge diverter Radio Interference measurements. BOOKS 1. Naidu and V. Kamaraju, high VOLTAGE engineering , Tata McGraw-Hill, 4th Edition, 2009. , Zaengl, and high VOLTAGE engineering Fundamentals , Second edition 2000, published by Butterworth-Heinemann , high VOLTAGE engineering , Third Edition, New Age International Publishers To Dedicated to all my students who made me learn this subject.

5 MODULE-I electrical materials constitute an extreme group of industrial materials that go specifically for manufacture of electrical machines, electrical apparatus, instruments, and other elements of electrical equipment and installations. By the behaviour in an electric and magnetic field, or both, we ordinarily categorize all of these materials into major groups. 1. Dielectric 2. Conducting 3. Semiconducting 4. Magnetic materials Reliability of product depend on quality of materials which are defined by the material characteristics electrical materials -> Thermal.

6 electrical , Atmospheric, Mechanical Magnetic materials -> Magnetic characteristics Mechanical characteristics -> Tensile strength Compressive strength Bending strength Elasticity electrical characteristics -> Resistivity Temperature coefficient of resistivity Dielectric Constant Electronic polarisation Dielectric polarisation Tan (loss tangent) Breakdown strength Atmospheric -> Viscosity Tropical resistance Acid number Thermal -> Melting point Softening point Heat stability Thermal Endurance 1.

7 CONDUCTION AND BREAKDOWN IN GASES The high - VOLTAGE power system, in general consists of a complex configuration of generators, long-distance transmission lines and localized distribution networks with above- and below-ground conductors for delivering energy to users. Associated with this are a wide range of high - VOLTAGE components whose successful operation depends on the correct choice of the electrical insulation for the particular application and VOLTAGE level. The condition of the insulating materials when new, and especially as they age, is a critical factor in determining the life of much equipment.

8 The need for effective maintenance, including continuous insulation monitoring in many cases, is becoming an important requirement in the asset management of existing and planned power systems. As the voltages and powers to be transmitted increased over the past hundred years the basic dielectrics greatly improved following extensive research by industry and in specialized high VOLTAGE laboratories, where much of this work continues. BACK GROUND MATERIAL Recollect kinetic theory of gases (Developed by Maxwell) PV=nRT where numerically R is equal to joules/ Kmol.

9 The fundamental equation for the kinetic theory of gas is derived with the following assumed conditions: Gas consists of molecules of the same mass which are assumed spheres. Molecules are in continuous random motion. Collisions are elastic simple mechanical. Mean distance between molecules is much greater than their diameter. Forces between molecules and the walls of the container are negligible. Gases as Insulating Media The most common dielectrics are gases. Many electrical apparatus use air as the insulating medium, while in a few cases other gases such as N2, CO2, CCl2F2 (freon) and SF6 (hexafluoride) are used.

10 Gases consist of neutral molecules, and are, therefore, good insulators. Yet under certain conditions, a breakdown of the insulating property occurs, and current can pass through the gas. Several phenomena are associated with the electric discharge in gases; among them are spark, dark (Townsend) discharge, glow, corona, and arc. In order to conduct electricity, two conditions are required. First, the normally neutral gas must create charges or accept them from external sources, or both. Second, an electric field should exist to produce the directional motion of the charges.